<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<style>
    .parent {
        width: 500px;
        height: 50px;
        padding: 20px;
        background-color: green;
        border: 1px solid #E74D4D;
        box-sizing: border-box;
    }

    .child {
        width: 100%;
        height: 30px;
        background-color: pink;
    }
</style>
<div class="parent">
        <div class="child"></div>
</div>
</body>
</html>
